In the books

In the A Song of Ice and Fire novels, Aggar's background is the same. He took part in the assault on Winterfell and the hunt for Bran and Rickon. Alongside Gelmarr and Gynir Rednose, he took part in the abduction and killing of the children whose corpses were passed off as Bran's and Rickon's. He, Gelmarr, and Gynir were secretly killed by Ramsay Snow at Theon's command, to prevent them from revealing the truth about the slain children. Farlen was falsely accused by Theon of the killing and was executed.